The present invention relates to transfer printing methods, more specifically, to the transfer printing method of printing images by a non-plate electronic print system onto a transfer material using sublimate ink, laying the transfer material ink-side down on top of a print medium, and transferring the print image from the transfer material to the print medium by heat processing the transfer material. The reproducibility of the colors of the transfer material transferred to the print medium is improved by controlling the print density of the yellow sublimate ink on the transfer material within a specific range of yellow density.
At present, mainstream transfer printing consists of two methods: the wet transfer method and the dry transfer method. Images are printed first on the transfer material such as paper and plastic film by screen printing or offset printing, then the images are transferred onto the print medium such as glass, metal, plastic or fabric by water, or by heat or pressure, respectively.
However, the above methods require the preparation of a print original for the purpose of screen printing or offset printing, which is time-consuming and costly. It is not suitable for low volume, multiple-type printing, and is impractical in adapting to an ever-changing demand by consumers for new and different designs.
In recent years, it has become very common to sell T-shirts and other merchandise prepared by the following process: Images are printed with a sublimate ink on the transfer material, then such transfer material is used to transfer various images onto T-shirts, aprons, luncheon mats, streamers, stickers, panels, coasters, and the like, by heat-contact printing which sublimates the ink, using an iron. Because of the vast range of consumers"" taste and style, which constantly change, there is a demand for low volume, multiple-type printing. This is not compatible with screen printing or off-set printing, which requires the costly and time-consuming preparation of a print original.
In light of such developments, a non-plate electronic print system has been introduced. Images created by digital cameras and scanners, and the like, are inputted to a personal computer (PC) and edited as desired. The images can be printed on the transfer material by an ink jet printer connected to the PC. The images, which are formed of sublimate ink, are then transferred onto the print medium using a heat iron. U.S. Pat. Nos. 5,047,084, 5,684,063, and 5,746,816 disclose such methods.
Such transfer printing using the non-plate electronic printing system permits very easy printing of images onto the transfer material and is suitable for low-volume, multiple-type printing. This method has become popular in recent years since it permits quick changes to meet changing fashion trends.
However, transfer printing using sublimate ink creates a large discrepancy between the colors first printed on the transfer material and those subsequently transferred onto the print medium from the transfer material. The ultimate color of the final images is very difficult to control when printing onto the transfer material. Repeated proof prints are needed to adjust colors prior to printing onto the print medium to provide reproducibility.
Such procedures are acceptable to a certain extent in transfer printing using screen printing or off-set printing, which are based on high volume printing. However, in transfer printing by the non-plate electronic print system for low-volume, multiple type printing, the process has been undesirable due to the disproportionate costs of set-up versus the revenue realized from the job.
It is desirable to increase the reproducibility of the color consistency of the transfers in order to minimize off-color prints prior to the final printing and to minimize the loss of print medium.
The present invention provides a transfer printing method for controlling the reproducibility of the transferred colors, and provides high density, high brilliance transfer prints, minimizing loss through off-color prints.
The present invention relates to the discovery that yellow sublimate ink undergoes little color change during the initial printing stage onto transfer material, as well as after transfer of the image onto print medium. The yellow density is transferred with stability among the three primary colors of red, yellow and blue during printing. It has been discovered that by maintaining the printing density of yellow sublimate ink within a specific range of yellow density during transfer onto transfer material, it is possible to enhance the reproducibility of high density, high brilliance transfer print images on the print medium.
The present invention comprises a transfer printing method which controls the printing density of yellow sublimate ink forming the image on the transfer material within a specific range of yellow density during the transfer print. Sublimate ink is printed onto the transfer material by means of a non-plate electronic printing system. The transfer material is laid on top of the print medium and the image is heat-transferred by sublimation of the ink from the image onto the print medium. The number of correction prints is reduced using the present invention. Reproducible, high density, high brilliance transfer prints are made by adjusting sublimate ink other than the yellow sublimate ink, which functions as the base color, based on images transferred onto the print medium. The yellow sublimate ink is controlled when applied to the transfer material to provide a high density, high brilliance transfer onto the print medium.
Additionally, the invention can prevent ruining the print medium along with ruined transfer material because such transfer material can be discarded when its yellow density of yellow sublimate ink does not fall within a specific range, before printing onto the print medium.
More specifically, it is desirable to control the yellow density on the solid printed area on the transfer material of yellow sublimate ink. Further, it is desirable to control the yellow density of the solid printed area within the range of 0.7-0.9. The density measurement is most accurate when measured on solid printed areas.
It is unlikely to obtain high density, high brilliance transfer prints on the print medium of various types when the yellow density is below 0.7 on the solid printed areas in the transfer material of yellow sublimate ink. Density over 0.9 causes images on the print medium to become blurry and the images themselves to be destroyed. Further, there may be frequent clogging of the nozzle of ink jet printers.
The yellow density described in the present invention means the yellow density measured by a densitometer manufactured based on JIS K 7654 xe2x80x9cPhotography, Density Measurement Part 4, Geometric Conditions for Reflection Densityxe2x80x9d (translation of ISO5/4, first edition, published in 1983), i.e. Gretag D 196 (trademarked) by Gretag-Macbeth AG. The print density ratio is the log of the intensity of the reflected light from the yellow density of the solid printed area divided by the intensity of the incident light.
Given below is the best mode of execution of the present invention. The present invention is not, however, limited by the following disclosure.
Sublimate Ink
The sublimate ink employed in the present invention is ink containing dyes which sublimate at certain temperatures, in this case, those temperatures achieved by a heating iron. The main components of sublimate inks are dyes, water, solvent and dispersant. Ink jet printer ink may be used.
The sublimate ink may be yellow ink, crimson ink, indigo ink and black ink, and are prepared by mixing the yellow sublimate dye, red sublimate dye and blue sublimate dye in proper proportions (See Table 1 below). In order to expand their range of expression, green, orange, violet and fluorescent ink may also be used.
For yellow sublimate dye, C.I Disperse Yellow 1, 3, 5, 7, 13, 23, 42, 51, 54, 61, 71, 82, 114, 141, 201 and E, as well as E-GRL can be used and, specifically, KAYASET YELLOW A-G (trademarked) by Nippon Kayaku Co., Ltd. is preferred. KAYASET YELLOW A-G has an absorption rate of 2.0/100 mg at 400 nm (xcexmax) and is commonly used as yellow ink as a solution containing solvents of dye concentration at 1-2 wt %.
For red sublimate dye, C.I. Disperse Red B, 1, 4, 17, 59, 60, 135, 167, and 210 can be used and specifically KAYASET RED B (trademarked) by Nippon Kayaku Co., Ltd., is preferred.
For blue sublimate dye, C.I. Disperse Blue 3, 14, 24, 26, 56, 92, and 106 can be used and, specifically, KAYASET BLUE FR (trademarked) by Nippon Kayaku Co., Ltd., is preferred.
The amount of water desirable as a main component in the sublimate ink is in the range of from about 10-93 wt %, preferably in the range from about 25-87 wt %, and more preferably from about 30-80 wt % of the total ink volume.
Suitable solvents include the organic solvents of ketone or ketone alcohol such as acetone and diacetone alcohol the concentration being from about 3-60 wt %, preferably from about 5-50% of the total ink volume. Other suitable organic solvents include alcohols, esters, ethers, and N-methyl-2-pyrolidone.
When dispersants are used, they may be used singly or in a mixture. The preferred dispersant contains solvent with a vapor pressure of about 0.1 mmHg or less (20xc2x0 C.). Such solvents may be single thioglycol, or diethylene glycol, propylene glycol and surface active agents alone or in mixtures.
Transfer Material
The transfer material for the present invention may be paper or plastic film, or specially designed paper for the sublimation transfer using ink jet printing. Specifically, the preferred sublimation transfer material available on the market is sold by Mitsubishi Paper Mills, Ltd.
Prints on Transfer Material
Printing of images on transfer material in the present invention is done by non-plate electronic printing system. Non-plate electronic printing system permits the use of a PC and an ink jet printer connected to the PC. For example, images are taken from a digital camera or scanner, and the like, edited, and then printed with sublimate ink onto transfer material by means of an ink jet printer connected to the PC.
The yellow density of the yellow sublimate ink on the solid printed area on the transfer material is controlled within the range of about 0.7 to 0.9. The yellow density is measured by using a densitometer directed at the yellow sublimate ink on the solid printed area. The print density ratio is the log of the intensity of the reflected light from the yellow density of the solid printed area divided by the intensity of the incident light.
Dr=Print Density by measuring light reflection for each color;
Lo=strength of incident light;
Lr=strength of reflection light;
Dr=log(Lo/Lr).
Suitable densitometers include Gretag D 196 (registered trademarked) by Gretag-Macbeth AG. The discharge volume of yellow sublimate ink from the inkjet printer or the volume of yellow dye in the yellow sublimate ink can be adjusted after the yellow density is measured to yield yellow density in the range of about 0.7 to 0.9.
Print Medium
The print medium used in the present invention may be, albeit not limited to, polyester cloth, T-shirts, aprons, luncheon mats, streamers, stickers, panels, and coasters.
Method of Transferring onto the Print Medium
The transfer material is laid print side-down, on top of the said print transfer medium. The transfer material is heat-pressed with hot press, iron, or the like, to sublimate the sublimate dye and to transfer the images on the transfer material onto the print medium. Normal transfer is achieved by heat pressing under the condition of 150-250xc2x0 C. for 10-120seconds, preferably for 20-60 seconds.
Using the yellow color of the yellow sublimate ink in the images transferred onto the print medium as a basis, the discharge volume of remaining crimson, indigo and black sublimate ink from the ink jet printer is adjusted or, alternately, the dye volume in the sublimate ink of said colors is adjusted.
In general, the four process colors for any printed matters have to be balanced in terms of color itself and color density for each of the four colors in order to reproduce the accurate and realistic image areas. Any photo pictures have to be reproduced exactly the same as the real images, simulating the original colors, regardless of the type of printing method. These can be realized by the balanced four process colors. Due to well balanced four color process colors in terms of color and density on printed matter, the three other colors can be automatically determined in terms of color and density, once the first color having a specific density gets chosen as the standard color. This invention discloses that yellow is found to be the best, and is the one chosen as the standard single color for ensuring reproducibility of print images in the ink jet sublimation printing system.
Yellow sublimate ink is used as a basis, the density of which is in the range of 0.7-0.9 on the solid printed area on the transfer material, while printing the images and the solid printed area on the transfer material using the remaining sublimate ink of crimson, indigo and black. The images and the solid printed area are transferred onto the print medium, the density of crimson, indigo and black being measured respectively on the solid printed area on the print medium using a densitometer, such as Gretag D-196 (trademarked) by Gretag-Macbeth AG. The volume of sublimate ink dyes can be adjusted, respectively, so that the crimson density is at 1.3-1.6, indigo density at 0.5-1.1 and black density at 1.2-1.8 while simultaneously fine-adjusting visually the crimson, indigo and black colors by using the yellow sublimate ink on the print medium as the base color.
By adopting the transfer printing method of the present invention, it becomes possible to radically reduce the number of correction prints prior to the print onto the print medium, as well as to minimize the number of failed print mediums.
The invention also permits printing on the transfer material by an ink jet printer based on a prior computer input of correction data on the ink jet printer discharge of the sublimate ink of the colors (crimson, indigo and black), in addition to yellow for respective print medium, if the yellow density of yellow sublimate ink on the solid printed area is measured and is confirmed that such density falls within the specified range.